Lecture 17 - Endocrine System 1 Flashcards
The endocrine system primarily maintains _____________ regulation of homeostatic imbalances via hormonal controls
Long-term
The endocrine acts with what system to coordinate and integrate the activity of body cells?
Nervous system
The endocrine system influences metabolic activities by means of _____________ transported in the blood.
Hormones
Responses of the endocrine system occur more slowly but tend to last longer than those of the _________________
Nervous system
Primary endocrine glands include pituitary, parathyroid, pineal and what other two glands?
Thyroid and adrenal
Some organs such as the ___________ and ___________ produce both hormones and exocrine products (sweat & saliva).
Pancreas and gonads
The ______________ has both neural and endocrine functions.
Hypothalamus
Long-distance chemical signals that travel in the blood or lymph
Hormones
Chemicals that exert effects on the same cells that secrete them
Autocrines
Locally acting chemicals that affect cells other than those that secrete them
Paracrines
______________ and _____________ are local chemical messengers and will NOT be considered part of the endocrine system.
Autocrines; Paracrines
2 main classes of hormones
Amino-acid based hormones and steroids
___________________ are amines, thyroxine, peptides and proteins
Amino-acid based hormones
_________________are synthesized from cholesterol. Examples include gonadal and adrenocortical hormones.
Steroids
True or false: Hormones can alter plasma membrane permeability of membrane potential by opening or closing ion channels on target cells.
True
True or false: Hormones stimulate synthesis of lipids or regulatory molecules on target cells.
False (proteins, not lipids)
True or false: Hormones activate or deactivate enzyme systems on target cells
True
True or false: Hormones induce secretory activity on target cells.
True
True or false: Hormones stimulate meiosis on target cells.
False (mitosis, not meiosis)
2 types of hormones
Water-soluble and lipid-soluble hormones
Water-soluble hormones are all amino-acid based hormones except ___________________.
Thyroid hormone
__________________ hormones cannot enter the target cells.
Water-soluble
Instead, water-soluble hormones act on ________________, coupled by G proteins to intracellular second messengers that mediate the target cell’s response.
Plasma membrane receptors
____________________ are steroid and thyroid hormones.
Lipid-soluble hormones
Lipid-soluble hormones act on _____________________ that directly activate genes.
Intracellular receptors
____________________ are transported into the cell and bind to nuclear receptors.
Thyroid hormones
One of the main signaling pathways activated by water-soluble hormones/ligands is the ____________________
cAMP signaling pathway
List the steps of the cAMP signaling pathway.
- Hormone (1st messenger) binds to receptor.
- Receptor activates G protein.
- G protein activates adenylyl cyclase
- Adenylyl cyclase converts ATP to cAMP (second messenger)
- cAMP activates protein kinases
- Activated protein kinases can phosphorylate other proteins or trigger other cellular responses.
Once cAMP is used, it is rapidly degraded by the enzyme ___________________.
Phosphodiesterase
Intracellular enzymatic cascades (of the cAMP pathway) have a huge ______________ effect.
Amplification
___________________ mechanism is used by some amino acid-based hormones in some tissues
PIP2-Calcium signaling
PIP2-Calcium signaling involves a G protein, which activates the enzyme _______________.
Phospholipase C
Phospholipase C splits the membrane phospholipid into 2 second messengers. What are they?
DAG and IP3
___________ activates protein kinases; ____________ triggers release of calcium (Calcium alters enzymes or channels or binds to the regulatory protein calmodulin).
DAG; IP3
Steps of steroid and thyroid hormone
- Diffuse into their target cells and bind with intracellular receptors.
- Receptor-hormone complex enters the nucleus and binds to a specific region of DNA.
- This prompts DNA transcription to produce mRNA.
- The mRNA directs protein synthesis
True or false: Target cells must have the specific receptors to which the hormone binds.
True
ACTH receptors are only found on certain cells of the _____________
Adrenal cortex
___________ receptors are found on nearly all cells of the body; it is the major hormone that triggers increased metabolism.
Thyroxin
Target cell activation depends on 3 factors:
- Blood levels of the hormone
- Relative number of receptors on or in the target cell
- Affinity of binding between receptor and hormone
Target cells form more receptors in response to the hormone
Up-regulation
Target cells lose receptors in response to the hormone
Down-regulation
Hormones circulate in the blood either free or bound:
- ___________ and ____________ are attached to plasma proteins
- All others circulate without carriers
Steroids; thyroid hormone
The concentration of a circulating hormone reflects the ______________ and speed of inactivation and removal from the body.
Rate of release
Hormones are removed from the blood by:
- Degrading enzymes
- Kidneys
- Liver
- Half-life
The time required for a hormone’s blood level to decrease by half
Half-life
One hormone cannot exert its effects without another hormone being present
Permissiveness
More than one hormone produces the effects on a target cell
Synergism
What is it called when one or more hormones opposes the action of another hormone? An example of this would be ________________.
Antagonism; insulin and glucagon
Blood levels of hormones are controlled by ______________ systems, and vary only within a narrow desirable range.
Negative feedback
Hormones are synthesized and released in response to these 3 types of stimuli.
- Humoral
- Neural
- Hormonal
Changing blood levels of ions and nutrients (metabolites) directly stimulate secretion of hormones.
Humoral stimuli
An example of humoral stimuli: declining blood calcium concentration stimulates the parathyroid glands to secrete PTH. PTH causes ________________ to rise and the stimulus is ________________.
Calcium concentrations; Removed
Nerve fibers stimulate hormone release
Neural stimuli
Example of neural stimuli: sympathetic nervous system fibers stimulate the adrenal medulla to secrete ______________.
Catecholamines
Hormones stimulate other endocrine organs to release their hormones
Hormonal stimuli
An example of hormonal stimuli:
- Hypothalamic hormones stimulate the release of most anterior pituitary hormones.
- Anterior pituitary hormones stimulate targets to secrete still more hormones.
- Hypothalamic-pituitary-target endocrine organ ____________ feedback loop: hormones from the final target organs ______________ the release of anterior pituitary hormones.
Negative; inhibit
The ________________ modifies the stimulation of endocrine glands and their negative feedback mechanisms.
Nervous system
Example of nervous system modulation: under severe stress, the hypothalamus and the _______________ nervous system are activated. As a result, body _________________ levels rise
Sympathetic; glucose
The pituitary gland (hypophysis) has 2 major lobes
Posterior and anterior
Posterior pituitary has pituicytes (glial-like supporting cells) and nerve fibers - more for storage of neurohormones _____________ and ___________.
Oxytocin; ADH
Posterior lobe is a downgrowth of hypothalamic ________ tissue.
Neural
The posterior lobe acts as a neural connection to the ________________.
Hypothalamus
Nuclei of the _________________ synthesize neurohormones oxytocin and antidiuretic hormone (ADH), which are then transported to the _________________.
Hypothalamus; Posterior pituitary
The anterior lobe originates as an out-pocketing of the _____________.
Oral mucosa
The anterior pituitary has a hypophyseal portal system, consisting of many capillaries. It contains a large amount of capillaries because its cells are better than the posterior pituitary at responding to ____________________.
Negative feedback loop
True or false: The hypothalamus carries releasing and inhibiting hormones to the anterior pituitary to regulate hormone secretion.
True
6 hormones of the anterior pituitary
- GH
- TSH
- ACTH
- FSH
- LH
- PRL
All anterior pituitary hormones are what type of compound?
Protein
All anterior pituitary hormones, except _________, activate cyclic AMP second-messenger system at their targets.
GH
TSH, ACTH, FSH, and LH are all ___________ hormones (regulate the secretory action of other endocrine glands).
Tropic
GH (Growth hormone) is produced by somatotrophs; it stimulates most cells, but targets ____________ and ____________.
Bone; skeletal muscle
GH promotes protein synthesis and encourages use of fats for fuel; most effects are mediated by ________________________.
Insulin-like growth factors (IGFS)
Low doses of GH in older age can help prevent ______________ by preventing muscle loss and osteoporosis.
Aging
GH is regulated by
Growth hormone-releasing hormone and growth hormone-inhibiting hormone (somatostatin)
GH directly stimulates liver, skeletal muscle, bone, and cartilage to produce _____________.
Insulin-like growth factors
True of false: GH directly mobilizes fats and elevates blood glucose by decreasing glucose uptake and encouraging glycogen breakdown (anti-insulin effect of GH)
True
Hypersecretion of GH results in _______________ in children and _______________ in adults.
Gigantism; Acromegaly
Hyposecretion of GH results in _______________ in children.
Pituitary dwarfism
__________________ is produced by thyrotrophs of the anterior pituitary.
TSH (Thyroid-stimulating hormone)
True or false: TSH stimulates the abnormal development and secretory activity of the thyroid.
False (normal, not abnormal)
TSH is stimulated by thyrotropin-releasing hormone (TRH). TRH is ________________ by rising blood levels of thyroid hormones that act on the pituitary and hypothalamus (negative feedback).
Inhibited
______________________ is secreted by corticotrophs of the anterior pituitary.
ACTH (Adrenocorticotropic hormone)
True or false: ACTH stimulates the adrenal cortex to release corticosteroids.
True
ACTH release is triggered by hypothalamic corticotropin-releasing hormone (CRH) in a __________________:
- -> Levels peak in the morning
- -> Rising levels of glucocorticoids feed back and block receptors of CRH and ACTH
Daily rhythm
Internal and external factors such as fever, hypoglycemia, and stressors can alter the release of __________________.
CRH
______________________ include FSH (follicle-stimulating hormone) and LH (luteinizing hormone).
Gonadotropins
____________________ are secreted by gonadotrophs of the anterior pituitary.
Gonadotropins
_____________ stimulates gamete (egg or sperm) production.
FSH
_____________ promotes production of gonadal hormones.
LH
True or false: Gonadotropins (FSH and LH) are absent from the blood in prepubertal boys and girls.
True
Gonadotropin release is triggered by the gonadotropin-releasing hormone during and after ________.
Puberty
Secreted by lactotrophs of the anterior pituitary
Prolactin (PRL)
True or false: Prolactin is primarily controlled by prolactin-inhibiting hormone (dopamine).
True
Blood levels rise toward the end of pregnancy. _____________ stimulates prolactin release and promotes continued milk production.
Suckling
True or false: If suckling is not induced, PRL is not released in great quantities and the woman will stop lactating within a week. Thus suckling is essential to PRL release.
True
